This invention relates to an improved method and electronic communication system for encoding and decoding data and for generating and discriminating analog signals to be used by modulators and de-modulators for transmission over various types of communications media.
A multitude of schemes have been used to send and receive data between two or more devices over many different medias. A typical transaction involves the entry of data by way of a keyboard, wand, reader or other input device to a computer or microprocessor. The data is formatted by the microprocessor and then presented to a circuit that provides an electrical interface to devices that provide modulation or process the signal to be compatible with the media used. The data is generally presented to a serial asynchronous or synchronous receiver/transmitter chip referred to as a UART or USART, followed by filters and other analog circuits that condition the signal for input to a modulator. There are many types of modulation schemes used to transmit the data, such as amplitude (AM), frequency (FM or FSK), phase (PM or PSK), pulse (PCM), and many variations and combinations of these. The modulation scheme is selected for the system requirements and media used, such as radio transmission, telephone lines, fiber optics, dedicated wires, infra-red and others.
The receiver demodulates the transmitted signal into an analog signal that is processed by interface circuits into a serial digital signal. The digital signal is presented to a UART or USART receiver resulting in digital data that is formatted by a microprocessor into an output understandable by an operator.
When evaluating the performance of a data communication system, factors to be considered are speed, data integrity, error rate, number of re-transmissions for a successful message, range, signal to noise ratios, distortion rejection, calibration, maintenance of complex hardware, cost, allowable system band width, and privacy or security. All of these factors, and even more, are inherent in any data communications system, without regard to the scheme used to encode and decode, and modulate and demodulate the data to be transmitted by the communications system.